1. Technical Field
The present invention relates to an arrangement for detecting X-ray radiations comprising a carrying member on one face arranged with detectors consisting of a plurality of sensors provided on a substrate. The invention also relates to an X-ray apparatus using such an arrangement and a method of scanning in an X-ray apparatus including such an arrangement.
2. Background Information
Typical X-ray imaging systems consist of an X-ray source in front of the object and an area detector behind the object for registering the image. However, this setup is sensitive to background noise in the form of Compton scattered radiation. Existing methods to remove this background noise are inefficient, and also tend to remove part of the primary X-rays containing the image information. This results in requiring a dose increase that may be as high as a factor of three (3).
One solution to this problem is a scanned-slot setup. With this solution, a pre-collimator slot before the object shapes the X-ray beam so that it matches the active detector area. The slot is mechanically moved in order to image the whole object. It is also possible to move or have the object move with respect to the slot. However, this can be inconvenient as the object is usually heavier than the mechanics for the slot. Still, the solution is advantageous since only a narrow fan-beam crosses the object at any single time, thereby minimizing the amount of Compton scattered X-rays. Another advantage with the scanned-slot approach is that the required detector area is much smaller. This reduces cost, and also enables the use of more expensive and efficient detector materials if desired.
A drawback with the scanned-slot geometry is that only a small fraction of the X-rays from the source is actually used to form the image. As a result, the time for image acquisition is extended, requiring the X-ray tube to be turned on for a longer period of time. A way of mitigating this problem and achieving a practical system is to use a multi-slot collimator with different detector arrays under each slot. However, this makes image acquisition difficult since information from the different detectors has to be combined together into one image without any visible artifacts, such as border lines between areas where different detectors are used.
U.S. Pat. No. 5,461,653 to Parker describes a filmless X-ray imaging system having at least one X-ray source, upper and lower collimators, and a solid-state detector array that can provide three-dimensional imaging capability. The X-ray source plane is distance z1 above the upper collimator plane, distance z2 above the lower collimator plane, and distance z3 above the plane of the detector array. The object to be X-rayed is located between the upper and lower collimator planes. The upper and lower collimators and detector array are moved horizontally with scanning velocities v1, v2, and v3, proportional to distances z1, z2 and z3, respectively. The pattern and size of openings in the collimators between detector positions is proportional such that similar triangles are always defined relative to the location of the X-ray source. X-rays that pass through openings in the upper collimator will always pass through corresponding and similar openings in the lower collimator, and then to a corresponding detector in the underlying detector array. Substantially all of the X-rays irradiating the object (and neither absorbed nor scattered) pass through the lower collimator openings and are detected, promoting enhanced sensitivity. A computer system coordinates repositioning of the collimators and detector array and X-ray source locations. The computer system can store detector array output and can associate a known X-ray source location with detector array output data, thereby providing three-dimensional imaging. Detector output may be viewed instantly, stored digitally, and/or transmitted electronically for image viewing at a remote site.
A method and apparatus for detecting X-ray radiation in a radiographic imaging context using “edge-on” detectors is disclosed in U.S. Pat. No. 4,937,453 to Nelson (“Nelson”). It is particularly useful in conjunction with slit and slot scan radiography. In accordance with this invention, detectors are constructed and arranged such that substantially all of the energy detected from an X-ray is discharged in the detector. In this way, a detector is provided that provides a direct electronic read out, high X-ray stopping power and high spatial resolution, while obtaining good signal collection efficiency without the use of excessively high voltage levels. In the preferred embodiment, solid state X-ray detectors are constructed such that the thickness of the detector along the direction of incident X-rays is long enough so that substantially all of the X-ray energy is discharged in the detector.
Pending Swedish Patent Application No. 9900856-7 (“the '856 application” ) refers to a method of obtaining improved radiographic images consisting of orienting a semiconductor radiation detector. The orienting step comprises selecting an acute angle between the direction of incident radiation and a side of the detector so that the incident radiation mainly hits the side.